At present, halogen-containing flame retardants (especially brominated flame retardants) are widely used in polymer flame retardant materials, and play a better flame retardant effect. However, it is concluded after the in-depth study of the fire scene that, although the halogen-containing flame retardant has a better flame retardant effect and a small addition amount, the polymer material containing the halogen-containing flame retardant will produce a lot of toxic and corrosive gas and smoke which suffocate people, thereby being more harmful than the fire itself. As a result, the development of the halogen-free flame retardant printed circuit boards has become a key point in the industry with the formal implementations of the EU Waste Electrical and Electronic Equipment Directive and the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment on Jul. 1, 2006. The CCL manufacturers have launched their own halogen-free flame retardant copper clad laminate.
Currently, phosphorus-containing resin is widely used in the industry to realize flame-retardant effect. But the introduction of too much phosphorus will make the water absorption of the substrate become high and the chemical resistance become worse. In recent years, the development of benzoxazine as a matrix resin for halogen-free substrate gets more and more attention. Benzoxazine is a benzo six-membered heterocyclic ring system composed of oxygen atoms and nitrogen atoms. It has the characteristics of ring-opening polymerization. When being polymerized, there is no release of small molecules. After polymerization, it is formed into a network structure similar to phenolic resin. The products thereof have small curing shrinkage, low porosity, excellent mechanical, electrical and flame retardant properties.
On the other aspect, with the rapid development of the electronics industry, electronic products tend to be light, thin, short, high density, security and high functionality, requiring electronic components to have higher signal transmission speed and transmission efficiency, which makes higher performance requirements on the printed circuit board as the carrier. Due to high speed and multi-functionalization of electronic product information processing, the application frequency is continually increased, and 3 GHz or more will gradually become mainstream, therefore, besides maintaining the higher requirements on heat resistance of laminate materials, dielectric constant and dielectric loss value will be required to be lower and lower.
The current traditional FR-4 is difficult to meet the application demand on high frequency and rapid development of electronic products. Meanwhile, the substrate material no longer plays the traditional mechanical support role, and will become together with the electronic components an important way to improve product performances for PCB and designers of terminal manufacturers.
Because high dielectric constant (Dk) will slow down the signal transmission rate, and high dielectric loss (DO will convert the signal partly into heat loss in the substrate material, high-frequency transmission with low dielectric constant and low dielectric loss, especially the development of halogen-free high-frequency plates, has become the focus of copper clad laminate industry.
In order to solve the above-mentioned problems, CN101684191B discloses that a cured product can be obtained by co-curing epoxy resin by using benzoxazine, styrene-maleic anhydride and phosphorus-containing curing agent. But there will inevitably be many other aspects of problems by reducing the dielectric properties of the material using only styrene-maleic anhydride. The impact on adhesion is particularly significant because the non-polar styrene structural unit in the molecular structure of styrene-maleic anhydride (SMA) decreases the polarity of the matrix resin, weakens the interaction between the resin and copper foil. At the same time, the large amount of benzene ring structure in SMA increases the brittleness of the resin crosslinking network, and also has adverse effect on the bonding performance under dynamic conditions, thereby reducing the bonding strength between the substrates and between the substrate and copper foils.
CN100523081C discloses that a cured product having a lower dielectric constant and dielectric loss can be obtained by co-curing phosphorus-containing epoxy resin with benzoxazine, styrene-maleic anhydride and other curing agents. However, although phosphorus-containing epoxy resin as the matrix resin can achieve excellent flame retardancy, the introduction of too much phosphorus will necessarily have a great impact on the water absorption of the substrate, which will certainly have negative impact on many other properties of the sheets.
CN103131131A discloses that a cured product having a lower dielectric constant and dielectric loss can be obtained by co-curing epoxy resin with benzoxazine, styrene-maleic anhydride and amine curing agent. Although ordinary benzoxazine can achieve the objects of curing epoxy resin and flame retardancy, it has a higher dielectric constant and is hard to meet the high-frequency high-speed transmission. Moreover, though the introduction of amine curing agent can enhance the adhesion property, the deficiencies of higher hygroscopicity and insufficient heat resistance for curing epoxy resin will necessarily have adverse effect on the use in high multi-layer circuit boards.
Therefore, it is an urgent problem to be solved how to produce prepregs and laminates having low dielectric constant, low dielectric loss and excellent chemical resistance.